Automated processing of biological samples typically involves the use of sample tube racks that are adapted to hold a relatively large number of sample tubes for processing within a sample preparation or test instrument. Generally, these sample tube racks are configured to enable the sample preparation or test instrument to hold and/or convey the rack, as well as any sample tubes disposed in the rack, throughout the preparation and/or testing process(es).
Sample tubes containing biological sample material are often sealed with a cap to minimize or prevent the possibility of contamination of the samples, other nearby samples and/or exposing instrument operators processing the samples to the biological material in the samples. However, with many known automated sample processing instruments, such sample tube caps must be removed from each sample tube prior to loading a rack of such tubes in the instruments. Of course, removing the caps can result in contamination of samples and/or exposure of instrument operators to the biological material in the samples.
To eliminate the problems associated with having to remove sample tubes caps prior to processing the sample tubes, some automated sample processing instruments are configured to work with sample tubes having penetrable or pierceable caps. In these instruments, disposable pipettes may be used to pierce the sample tube caps, thereby reducing the possibility of sample contamination and/or operator exposure to biological material. While such automated instruments can eliminate significant amounts of mechanical manipulation of the samples and offer a significant improvement in contamination or exposure issues, proper retention of the sample tubes in the rack becomes an important consideration because withdrawal of the pipettes from the pierceable caps may tend to lift the sample tubes out of the rack due to the frictional forces between the caps and the pipettes.
Further, the use of pierceable caps on sample tubes can also result in pressure differentials between the contents of the sample tube and the ambient in which the caps are pierced. For example, if a sample is collected and capped at a relatively low altitude location and subsequently processed (i.e., the cap is pierced) at a higher altitude location, fluid and/or aerosols containing biological material may be expelled out the pierced opening in the cap, thereby potentially contaminating other samples and/or exposing instrument operators to the biological material.